Cholinergic-adrenergic interactions on intestinal ion transport.

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Abstract
The autonomic control of intestinal electrolyte transport was investigated in the in vitro, short-circuited rabbit ileum with varying doses of carbachol and with neuroeffector blocking agents. Low-dose carbachol (< 10-6 M) and high-dose carbachol (> 10-4 M) had different effects on Na and Cl transport. Low-dose carbachol caused a transient increase in the potential difference and short-circuit current, stimulated Cl secretion and inhibited the residual flux (probably HCO3 secretion). This is a muscarinic response since it is inhibited by atropine (10-6 M). After an initial increase of the potential difference and short-circuit current, high-dose carbachol reduced these electrical parameters, stimulated Na and Cl absorption and abolished the residual flux. This is a nicotinic response since it is inhibited by hexamethonium (10-5 M). This nicotinic response is identical to that reported by others with .alpha.-adrenergic agents and it was inhibited also by phentolamine (10-7 M). High-dose carbachol may stimulate nicotinic receptors on postganglionic sympathetic fibers present in the preparations causing a release of catecholamines and a resulting .alpha.-adrenergic response by the intestinal epithelial cell. The physiological significance of this response in the gut remains to be determined.